Establishing a collection of ripening bacteriophages isolated from cheese: insights from the surphages project.
Résumé
Bacteriophages are significant biological entities in the dairy industry due to their impact on cheese production. While existing collections of dairy-phages primarily consist of phages infecting lactic acid bacteria (LAB) used as starter culture for milk acidification in the first step of cheese production, recent research has revealed a broad diversity of phages that also target non-starter LAB in cheese, including ripening bacteria. These bacteria play a crucial role in the maturation process by producing pigments, flavors and aroma compounds, thus contributing to the cheese’s tipicity. To fully understand the biology of these newly discovered phages and their potential effects on cheese quality, whether positive or negative, further efforts are needed to isolate and characterize representative phages from this diverse group. The main objective of the Surphages project is to address this gap by establishing a large collection of phages isolated from cheese that infect ripening bacteria, and by describing their diversity across different cheese technologies. In the first steps of the project, viral fractions were purified from the rinds of several French cheese varieties and analyzed using epifluorescence microscopy to estimate the concentration of virus-like particles (VLPs) in cheese. In addition, a bacterial collection was recovered from the same samples, with a focus on Brevibacterium, Propionibacterium, Leuconostoc, Hafnia, Staphylococcus, Corynebacterium and Glutamicibacter genera, which were then used to isolate phages through a double-layer spot assay. Initial results indicate that viral load (particles per gram of cheese) varies greatly between cheeses, with differences of up to 3 logs. Moreover, several lysis plaques have already been observed using the culture-dependent approach on the first samples. After purification and dereplication, we aim to collect between 50 and 100 distinct phages, which will be further characterized using transmission electron microscopy and genome sequencing. This new phage collection will provide a valuable resource for the dairy industry to assess the impact of dairy phages on production processes.
